Reynolds, G.D. & Richards, J.E. (2004). Cortical source localization of infant visual attention and recognition memory. International Society for Infancy Studies, Chicago, IL.
Early studies of the development of recognition memory in infants demonstrated a negative component over central leads (Nc) with greater amplitude in event-related potentials following presentations of a novel stimulus than presentations of a familiar stimulus. In contrast, subsequent investigations utilizing a familiarization phase prior to stimulus exposure found that Nc amplitudes do not vary significantly following novel versus familiar stimulus presentations. Recent research has demonstrated that attention affects ERPs associated with recognition memory. The present study investigated the effects of familiarization and attention on electrophysiological correlates of recognition memory in infants. Seventy infants in the following three age groups were used as participants: 20, 26, and 32 weeks of age. Two familiarization groups were utilized: familiarization and familiarization control. Infants in the familiarization group were familiarized with two stimuli that were used during testing, infants in the familiarization control group were familiarized with two stimuli that were not used in subsequent testing. Following the familiarization phase, infants were exposed to a modified-oddball paradigm with presentations of three types of memory stimuli: frequent familiar, infrequent familiar, and infrequent novel. Electroencephalographic recordings were made with a 124-channel system and ERP averages were made from -50 ms to 2000 ms around stimulus onset. The ERP were quantified with spatial independent components analysis, and equivalent current dipoles" were estimated to locate cortical sources of the ERP components. Heart rate was measured as an index of attention. A negative component (Nc) was found to occur about 500 ms after stimulus onset. The cortical source of this component was located in areas of frontal cortex including the middle frontal gyrus inferior frontal gyrus and anterior cingulate cortex. Infants in the familiarization group demonstrated greater amplitude Nc components following novel stimulus presentations than familiar stimulus presentations. The familiarization control group did not display differences in the amplitude of Nc for stimulus type. Nc amplitude was greater during periods of attention than during periods of inattention. Age differences were found in late slow wave components for memory stimulus type. These findings suggest that familiarization attention and stimulus type impact ERPs associated with recognition memory in infants.